Superheterodyne receivers (also referred to herein as “super-het” receivers) are advantageously used in a variety of contexts, such as radio communication, since such receivers employ frequency mixing to convert a received signal (e.g., from an antenna) to a fixed intermediate frequency (IF) that can be more conveniently processed than the original carrier frequency of the received signal.
While super-het receivers are widely popular and offer many advantages, known super-het receivers are unsatisfactory in a number of respects. For example, such receivers are subject to various categories of noise, such as spurious noise outside the detection bandwidth of the receiver. As used herein, the phrase “spurious noise” refers to any signal energy that is not the signal of interest. Examples of such noise are limitless and cover the entire electromagnetic spectrum, ranging from natural sources such as radio waves from space to man-made sources such as microwave ovens or airport radars. Such external sources of noise, regardless of their source or frequency (outside the final detection bandwidth), should not impair the final fidelity of the detection of the signal of interest. Prior art attempts to design super-het receivers that are immune or substantially immune to spurious noise have largely been unsuccessful as they do not employ an optimum combination of filters, mixers, and oscillators (such as local oscillators).
Accordingly, methods and systems are desired for superheterodyne receivers with improved spurious noise immunity.